1. Field of the Invention
The present invention generally pertains to a system for cooling electronic components mounted on an electronic component rack. More particularly, the invention pertains to a forced air electronic component cooling system which utilizes several fans and selectively configured air deflectors to provide uniform cooling of electronic components within a multilevel electronic component rack.
2. Description of Related Art
Electronic equipment, such as communication or computing hardware, typically comprises a plurality of printed circuit boards which are mounted within a shelving unit. Typically, a plurality of shelving units are stacked one upon the other in an enclosure. Enclosures are required in an outdoor environment to prevent environmental hazards such as rain, snow, sleet and flying debris from damaging the electronic components. For indoor environments, enclosures are used to prevent inadvertent damage to electronic components by people working in the vicinity of the enclosures.
One of the critical factors in maintaining a proper ambient environment for electronic components, whether outdoor or indoor, is to maintain the temperature of the enclosure within a desired operating range. The printed circuit boards must be cooled to ensure proper operation of the electronic circuits and to prevent premature electronic component degradation and failure. Since the number of electronic circuits on each printed circuit board has increased exponentially with the advance of VLSI circuit design, the thermal density of the printed circuit boards has also greatly increased. Providing adequate cooling for all printed circuit boards within an enclosure has become problematic.
To maintain cooling for a shelving unit which accommodates a plurality of printed circuit boards exhibiting a high thermal density, forced air cooling structures having fans are typically used. In this type of cooling structure, an important factor for realizing effective heat removal is not only the temperature of the cooling air which removes the heat from the circuit board, but also the velocity of the air flow.
There have been attempts in the prior art to address the cooling problems. For example, U.S. Pat. No. 3,967,874 discloses a printed circuit board mounting assembly which provides uniform cooling for an array of printed circuit boards. A fan is provided for each card cage, with each cage having a plurality of printed circuit boards mounted therein. A high velocity centrifugal fan blows air into in a plenum having a perforated screen. The screen is configured to include a series of crests and troughs which cause air turbulence. This uniformly directs the air flow through the screen and past the printed circuit boards. Although this assembly ensures adequate cooling by providing a separate fan for each printed circuit board cage, loss of the fan may result in severe damage of the printed circuit boards in that cage due to thermal overloading.
U.S. Pat. No. 4,399,485 discloses an air baffle assembly for mounting in a printed circuit board cage. The baffle maintains a constant uniform impedance to the flow of cooling air across a vacant space on a partially populated electronic mounting frame for printed circuit boards. The baffle assembly includes end boards mounted on opposite sides of the vacant space and a web member which extends between the boards. The web member has a plurality of small apertures to approximate the impedance presented by populated portions of the frame. This assembly utilizes a single fan to cool the printed circuit boards. Accordingly, failure of the fan would result in eventual failure or damage to the electronic components.
U.S. Pat. No. 4,774,631 discloses a cooling structure having a plurality of fans for cooling an electronic equipment rack. The structure comprises a plurality of shelving units stacked one upon the other. Each shelving unit has upper and lower venting apertures and accommodates a plurality of printed circuit boards. Each shelving unit is divided into a plurality of separate cooling blocks. The fan for each cooling block generates a flow of air through a portion of the shelving unit from bottom to top. Use of separate cooling blocks increases the risk that failure of the fan will result in degradation to components within that cooling block.
Accordingly, there exists a need for a forced air cooling system which provides adequate flow to each of the electronic components in an enclosure while providing redundancy in the case of fan failure.